Present Open-Chamber, or Direct Injection (DI) type diesel engines face major environmental pressures. Several sophisticated technologies are being used; such as four-valves; single or double overhead camshafts (SOHC or DOHC); electronically-controlled high-pressure injection, turbocharging and aftercooling. These technologies are now reaching a point of diminishing returns and are no longer capable of delivering the manifold emissions reductions necessary for future engines. Also, new solutions being sought such as injection timing using multiple injections (both before and after the main injection-period); exhaust-gas recirculation (EGR); fuel injection into the exhaust manifold, soot traps and selective catalyst reduction (SCR) are essentially add-on technologies alien to the basic engine.
The aforementioned technologies, in varied degrees, are either bulky and expensive, or create excessive back-pressure which reduces the power output while increasing the fuel consumption; or increase the emissions of soot and PM to reduce the emissions of NOx; or require expensive urea injection into the exhaust stream; or increase engine wear and reduce durability. In summary, they reflect a basic impossibility of solving the combustion problems of today's engines.
Most of today's high-speed DI engines use swirl as a main combustion accelerator. The swirl concept is old and has become nearly universally used especially after the 1950's. During the last fifteen years, high-pressure injection has been used and partially reduces the need for providing swirl. Swirl decreases the air flow and consumes much pressure energy as it is induced through long helical intake ports. This undesirably produces ports with high surface to volume (S/V) ratios. The air flow through these long ports; and the increased exposure of the air to the hot engine coolant through the port walls, raises the temperature of the air entering the cylinder during the intake stroke and, once inside the cylinder, the swirling air scrubs the hot walls, piston and cylinder head; further increasing the air temperature. The increased temperature lowers the density and mass of the air; thus reducing the air throughput and power output of the engine. The situation is aggravated because the engines cannot use high degrees of overlap to scavenge the cylinder of the exhaust gas residuals left over from the previous combustion cycle, or to cool the chamber and start the new induction process with fresh air which, at lower temperature and with higher density, increases the air mass. High overlap is not used because it forces valve-relief pockets (notches) on the piston top; and the notches interfere with the swirl. Therefore, further power losses are incurred, with increases in fuel consumption and emissions (NOx, Hc, soot, PM and smoke). The increased soot and smoke, in passing through the piston rings, increase the piston, ring, ring groove and liner wear while contaminating the oil; forcing more-frequent oil and filter changes. Lacking the cooling benefits of overlap, those same components, plus the turbocharger; run hotter, reducing their life.
There are benefits of valve overlap as generated by an early intake valve opening (IVO) and a late exhaust valve closing (EVC). One benefit is that, with an earlier IVO it is also possible to use an intake valve closing (IVC) earlier than possible with current engines. This reduces the amount of air that flows back-out of the cylinder through the still-open intake valves (called backflow or spit-back) as the piston passes BDC and starts the compression stroke; which is especially a problem with late IVC during engine starting and at low-speeds. An early IVC improves the cold startability and the idle quality by increasing the trapped air mass (TAM) and the effective compression ratio (CRe).
The diesel engine process has always been thought to require high compression ratio to initiate combustion of the injected fuel. This is a very-simplistic approach and normally a higher ratio is provided than needed for normal operation. In SAE Paper 2001-01-0271; titled “The Case for New Divided-Chamber Diesel Combustion Systems”, Part One: Critical Analysis of Current DI and Past Significant Divided-Chamber Engines; presented to the 2001 SAE World Congress in Detroit, Mich.; Mar. 5–8, 2001; I discussed many earlier engines that demonstrated that high Nominal Compression Ratio )CRn) was only needed for starting cold; not for normal operation. Furthermore, in two companion papers (SAE 2001-01-0274 and 2001-01-0278, presented to the SAE Congress on the same day) I proposed that what is needed for good cold startability and good, smooth, quiet idle is neither high CRn nor high air temperature; but high Enthalpy of the TAM. The higher Enthalpy results from the increase in energy (temperature and pressure), during compression of the increased TAM in the cylinder, utilizing an IVC earlier than what is used today. The combustion-philosophy changes, which can also be enhanced by additional injection-timing retardation, reduce the delay time of the fuel, for improved combustion initiation and startability, and also reduces the combustion noise (Diesel Knock), as less fuel is ignited simultaneously because less fuel is injected during the shorter delay period. The softer, more-retarded initiation of combustion also reduces the NOx, soot, PM and smoke emissions. Additionally, part of the negative combustion work (work on the piston as a result of combustion before TDC); which is eliminated and produces improved Mechanical Efficiency (automatically reducing the fuel consumption); as well as reduced firing pressure (Pmax) and the rate at which the cylinder pressure increases (Rate of Rise, or ROR). Still more, today's common wisdom ignores the effects of both the increased CRe and TAM. This is a philosophical engineering riddle; for, to maintain the high CRn, designers do not want to create the piston pockets which allow the intake and exhaust valves to obtain partial lift; freely and simultaneously, as they “cross” during overlap without hitting the piston. One reason is that, as already mentioned, the piston pockets interfere with the carefully-orchestrated swirl; and another is that the pockets create volumes which increase the combustion chamber's Clearance Volume (Cv); which of course reduces the CRn. The fact that with deeper intake pockets atop the piston, the increases in CRe obtained by advancing the intake-valve events and having the valve(s) lift into the piston pockets are, to a point, larger than the losses of CRn has also been ignored. On paper 2001-01-0278 a chart (labelled FIG. 1) clearly indicates that, up to a point, the CRe increase more than compensates for the CRn reduction; and that the TAM increases, for the particular example, from 72% to 95% of the cylinder volume; this being the reason for the improved startability of the test engine.
We should not ignore that, by reducing the CRn while advancing the IVC on one of today's engines it is possible to maintain the CRe while reducing the chamber's S/V and increasing the TAM; thus further improving the startability and idle quality of the engine.
Additionally, another beneficial effect of overlap is also ignored; which is that it improves the high-speed, high-load gas exchange and eliminates the potential recompression spike of the exhaust gas trapped in the cylinder, which effectively increases the negative cylinder-work and robs the engine of usable power output while increasing the fuel consumption, emissions, ROR and Pmax. With the new air-cycle philosophy of this invention, one of the basic tenets is to solve the fundamental combustion problems without swirl; as swirl imposes far too many undesirable compromises. The elimination of swirl, and the increase in valve overlap, are sufficient to categorize the new combustion process which produces major thermodynamic improvements in engine operation. This is especially so as the changes can be simply obtained by advancing the intake camshaft or intake cam lobes and forming valve-relief pockets in the pistons.
A problem being faced by today's trucking industry is the inability of hiring, and retaining, professional drivers. The situation has become so difficult that many trucking companies are now doing their long-distance shipping by rail. This, of course, makes them share their earnings with the railroads, and reduces their profits. The sale of trucks, and engines, by the Original Equipment Manufacturers, also suffers; as well as the funding to continue doing engine research. Part of a driver's dissatisfaction stems from the constant need to shift gears; because it is tiring, distractive, time-consuming, dangerous and wears-out the drivetrain. To compensate, and ease the driver's load, engines for Class Eight trucks are being produced with up to 600 HP. This, of course, is very expensive. What is needed is engines with “constant horsepower” (or high torque-rise). If an engine rated at 2000 rpm can increase its torque by 50% (50% torque rise or torque back-up) while lugging its speed down to 1000 rpm; it achieves “constant horsepower” between 1000 rpm and 2000 rpm. This is extremely important, for a truck can then climb hills without shifting gears utilizing a simpler, cheaper, lighter and more-efficient transmission with less gear-ratios; for less wear and tear on the equipment and the driver and reduced overall cost, as high-load operation at low speed also reduces the fuel consumption and emissions. With today's turbocharging technologies, including electronically-controlled Variable Area Turbines (and maybe also compressors) or waste-gates; plus common-rail fuel injection systems, a tremendous amount of air can be processed at low-engine speeds, and the necessary fuel to burn it can also be handled. Both of these technologies can go a long-way towards the desired “constant horsepower” engine; what is missing, however, is the ability to retain all that air in the cylinder by preventing low-speed backflow. This can only be achieved by using early IVC. Early IVC, by advancing the intake events on an otherwise “fixed timing camshaft”; or by using variable-valve timing (which also produces a Variable Effective Compression Ratio—VECR—and increases low-speed TAM), is impossible if the valve(s) interfere with the piston during overlap and notches are not provided. Early IVC, and the resultant higher CRe with CRn reduction also reduces the sensitivity to manufacturing tolerances. Unfortunately, none of these benefits can be obtained with today's engines because the required deep piston notches destroy the swirl. The reduction or elimination of swirl then becomes necessary to operate the engine with a better thermodynamic air-cycle and to produce a new type of torque curve, using other means of accelerating the combustion process; as proposed in this application.
The new combustion system as described in this application is intended to replace current combustion technologies; both the newest direct injection (DI) and the older divided-chamber designs. This new system must be more efficient than swirl in generating a combustion-acceleration process; and thus, it will not have to accelerate all the air into any kind of forced, unnatural motion. The intake air will not gain as much heat or lose as much pressure from flow through long tortuous intake ports and along cylinder walls and, finally, since combustion will occur only primarily after TDC, the combustion-acceleration process will take place only primarily after TDC. To achieve this new air-cycle philosophy and combustion system, piston notches; to prevent piston-to-valve interference during overlap, are provided. To achieve a faster, more efficient combustion process than those of older divided-chamber systems, the restriction between the divided-chamber and the main chamber must be reduced; the mixing of air and fuel inside the divided-chamber must be improved; and the discharge of products of divided-chamber combustion into the main chamber must be faster and more efficient; with less pressure and temperature losses and with improved coverage of the main-chamber volumes.
A new fuel system is also necessary to provide variable fuel flow at the beginning of injection, so as to avoid an excessive amount of fuel injected during the ignition delay, to reduce the noise and NOx; yet, once the delay is completed, and the fuel quietly ignited, the fuel flow rate must be increased, to, in combination with the combustion acceleration feature generated and used quickly only after TDC, rapidly complete the combustion process to improve its efficiency. This will limit the ROR and Pmax; to allow more load (air) to be carried into the cylinder, so as to produce more power without reaching the Pmax levels that engines are encountering today; levels which force the use of stronger, heavier, more-expensive components. The new combustion process would increase the Mechanical Efficiency of the engine, to increase the power output and Thermal Efficiency; while reducing the emissions of NOx, PM, smoke, soot and noise.
Some old divided-chamber engines showed some desirable combustion characteristics. The Lanova combustion system, discussed in the aforementioned SAE Paper 2001-01-0271, provides one example. Lanova placed a horizontal injector, transversely to the engine centerline, in the lower part (fire-deck) of the cylinder head, and a single-orifice energy-cell opposite to it, on the other side of the cylinder, also either horizontally or at a slight upward inclination from the horizontal; the inclination forced upon by physical difficulties. On these two-valve 1930's engines, a main-combustion chamber was formed in the cylinder head; between the injector and the energy-cell. The chamber was formed by deeply recessing both the intake and the exhaust valves into the cylinder head; for a so-called “Dual-Lobe” design used mostly on industrial, truck and bus engines. Later, the “Single-Lobe” design was adopted for smaller engines which could not obtain the desired CRn with two lobes; on these smaller engines, only the intake valve was recessed. The deep intake valve recession, and the “lobe” thus formed, provided enough vertical space to locate the injector and the Energy-Cell in the cylinder head; far-enough away from the fire deck so that there was sufficient metal thickness between it and the injector on one side, and the Energy-Cell on the other. With either the single or dual lobe designs, the large valves which were typical of the Lanova engines overlapped the engine's bore and thus took advantage (at least in the case of the single intake lobe) of the lobe's great depth; allowing the intake valve to open fully into it without hitting either the block or the piston. With such freedom, the intake valve could have many possible timing characteristics and thus advanced intake-valve timing; with early IVO and IVC. The injector typically used a throttling-pintle nozzle tip which limited the amount of fuel injected up-front, during the delay period, to obtain extremely good, smooth, quiet cold starts; and then, after ignition, sprayed the main bulk of fuel typically on a 4° cone. The periphery of the cone would “peel-off” as it crossed the main chamber, and mix with the air in it; igniting while airborne. The core of the fuel plume would continue, and enter the energy-cell to burn with the air present therein. Injection would typically begin a few degrees before TDC, timed so that, with the cylinder air at near maximum compression temperature, combustion of the spray cone would start around TDC. The subsequent violent combustion in the energy-cell, utilizing only a small portion of the combustion air, produced a strong reflux of burning products back into the still-flowing fuel-injection plume in the intake lobe; to break it up and mix it with the air, while producing a swirl action within the intake lobe and complete the burn very quickly while the injection lasted. On “Dual Lobe” systems, the fuel plume would be pushed backwards against the injector, forming two counter-rotating swirl streams inside both “lobes” as the piston started on its expansion stroke. This unique, strong and fast combustion-acceleration mechanism did not waste energy by inducing swirl on all the air in the cylinder, typically a full revolution before combustion (during the intake stroke). It also did not waste energy by starting the combustion process long-before TDC, and creating negative work. It, therefore, yielded a cycle better described as being of “Constant Pressure”. The Lanova system, with its late but fast combustion; and relatively low Pmax, allowed light engines (sometimes actually based on gasoline-engine blocks and cylinder heads) to be converted to simple diesels quickly and cheaply, with minimum development; something very critical during the Depression, WWII and the Post-War period. The specific issue of fuel consumption of all the diesels; included Lanovas, was not a priority then. Although high by today's standards, it was good-enough then, using almost half as much fuel (and of lower cost and higher thermal energy) than the competitive gasoline engines which, with low Compression Ratios, poor “L” head combustion chambers, and with leaky carburetors, wasted and spilled and incredible amount of expensive fuel. The Lanovas also had incredibly smooth and quiet cold-starting and idling characteristics. For years, well into the 1950's, much philosophical controversy abounded about how the engines could accomplish such feats, and also exhibit low ROR and Pmax ; especially when the compression ratios (CRn) were seldom higher than 12.4:1; when the chamber's S/V was so high; and when the energy-cell had such large thermal losses as it also had very-large S/V and was made of steel (with high Specific Heat and Heat Transfer Coefficient). In fact, the problem is still incomprehensible to many. The issue whether combustion started in the energy-cell or in the main chamber was debated for decades, almost to the dying days of the system, and was never fully-explained, In retrospect, it seems that our ancestors were pretty happy with what they had and were not interested in really finding-out why. It was truly a great technical loss that they never found-out why the engines performed, thermodynamically, as they did; for if the true reasons had been found-out, the path of diesel engine technology could have been changed dramatically; by improving designs based on those findings. I have insisted, for many years (and finally demonstrated as explained in the three SAE papers of reference) that the root base of all the unexplained phenomena was that the engines had very-good overlap (in the dual-lobe system), or at least, early IVC (in both the dual and single-lobe types); and that it was the increased TAM and very-high CRe (from early IVC); with higher Enthalpy in the air at the moment of injection, that was the secret behind it all. The overlap (and early IVC) were not easily noticed because the valves were recessed into the “Combustion Lobes” and did not require valve-relief pockets on top of the pistons. To the casual observer, the fact that overlap was present was not obvious. And, as a consequence, the early IVC went unnoticed. There is strong evidence that even the Lanova Corporation, or its owner, the brilliant inventor Frantz Lang, did not understand the phenomena, for they never advertised it or even wrote about it (or improved the design as I am doing now); instead argued for years (and changed opinion twice) about combustion started in the energy-cell or in the main chamber.
The Lanova combustion system, on the other hand, was not applicable to four-valve engines; it would have required major modifications to survive to the present day (modifications such as I am proposing now). It had high thermal losses from the high S/V and poor materials in the energy-cell; and suffered major problems with mechanical failures from the thin metal sections in the cylinder head fire-deck; below the horizontally-placed injector and energy cell. Also, the relatively unsophisticated fueling of the energy-cell; and the fact that the distance between the injector nozzle tip and the transfer passage into the energy-cell was constant, under some operating conditions allowed a large excess of fuel to enter the cell. This could create very-rich mixtures with the limited air-mass within the cell, forming heavy soot therein. The soot ultimately filled the cell, rendering it ineffective, and required frequent maintenance to remove it. With all these problems, the Lanova system carried the seeds of its own destruction.
Another interesting old engine of the 1930's was the 6 l, six cylinder M.A.N. used by the German Military during WWII; also described in the aforementioned SAE reference paper 2001-01-0271. This engine had what, on first sight, looks like a very-odd and ugly combustion system. Its operation, however, indicates that it was well thought-out to do the required military job at the time. This engine also used a throttling-pintle nozzle type injector; (its cone angle, if any, unknown). The injector was placed at a slightly-inclined angle in the cylinder head,; at the small (top) end of an odd inverted-funnel upward-extension of the chamber, what I call the “fuel funnel”. While the long fuel funnel maintained the fuel plume discharged by the nozzle tip airborne during ignition and combustion, it also increased the chamber's S/V; and its heat losses. On the lower, larger-diameter side of the fuel funnel, close to the main chamber, a separate auxiliary air-cell was disposed; communicating with the fuel funnel through three small transfer passages. Between the piston and the fire-deck there was only a thin “bump clearance”, with shallow valve-relief pockets, but with very-large surface area (and S/V). During compression, most of the air would fill both the fuel funnel and the auxiliary air-cell; after ignition, the air-cell, which no fuel entered, would cushion and dampen the rapid ROR and high Pmax; then, later, the air in it would expand and exit to help evacuate the burning fuel and air out of the fuel funnel to; also, like the Lanova, provide an after-TDC combustion-acceleration mechanism for a quick end of combustion on the 2400 rpm engine (a fast speed, then). In spite of the extremely-high S/V ratio of the combustion chamber, the engines started extremely well; under any conditions, unaided by glow-plugs or any other means (which was why the German Military chose them over the competing Mercedes, which could not start cold at all without glow-plugs). That, in the 1930's, was an incredible accomplishment; especially since the relatively-small engine cylinders (105 mm bore×120 mm stroke; 1 l/cylinder), only had a CRn of 15.5:1. It is interesting that, today, DI engines of this size, with much-lower S/V than the M.A.N. engine; need a higher CRn to start cold; and many also use glow-plugs. What has surfaced is that the M.A.N engine; contrary to modern DI designs, used a very-early IVC, high CRe and TAM. If the long fuel-plume path inside the fuel funnel contributed to the incredible startability, this philosophy is also an integral part of my new combustion system. The M.A.N. engine, however, with the huge chamber S/V, lost a sizable portion of its compression and combustion energy to the cooling system, and, eventually, with reduced thermal efficiency, was also discarded. My proposed energy-cell solution does not incur the excessive thermal losses of the M.A.N. engine; to maintain a higher thermal efficiency without losing the effective ignition characteristics and smooth, quiet operation with low CRn.
Whereas piston notches are a perfectly understood necessity to obtain valve overlap for the common reason of cooling the chamber, turbocharger, etc.; the need for overlap (and piston notches) in order to advance the IVC without shortening the open-valve duration; for increasing the CRe, cannot be found in the literature. Even thus we have discovered that it has been used on many old engines: the literature does not indicate that the developers of those engines ever made the connection to improved startability; or quieter, smoother idle. In every case, the better startability or idle running was credited to some other engine feature, such as the chamber's, pre-chamber's, or energy-cell design, material or shape, or other injection characteristic; or the use of a starting system providing faster cranking speeds. The same situation occurs with the use of a later EVO for an improved expansion and exhaust process; when the true thermodynamic reasons are not understood. Although some obscure mention is occasionally made on the literature about the effects of a late EVO on increasing the effective expansion ratio (ERe), it is never linked to the overlap and the need for notches. In addition, the new term for Trapped Air Mass (TAM), which I have used for the first time and introduced in the literature (see my aforementioned SAE paper 2001-01-0278 published on Mar. 5, 2001) specifically indicates its linkage to the IVC point, and the need for overlap and also earlier IVO, without losing valve duration period; as a pre-requisite for additional benefits on cold startability and smooth, quiet idles and low-speed running; based on reduced ignition-delay periods. Improved startability, smoother idle and low-speed running, plus increased low-speed torque, based on reduced ignition delay; and derived from higher CRe and TAM jointly increasing the Enthalpy of the compressed air just-before injection, and as defined in the SAE paper mentioned above, is a whole new Thermodynamic concept.
Since the early day of diesel engines, the piston rings were placed at safe distances from the top of the pistons, to keep them from running too hot under high load/speed conditions; in the poorly-lubricated area near the top of the cylinder. The poor quality of the piston, piston rings and cylinder (or liner) materials at the time resulted in high wear on all three. The low position of the ring-pack in relation to the piston top, and the reduced temperature therein, kept the rings from “sticking” with soot, and losing their sealing ability. This problem, on DI engines with Hesselman (mexican hat) pistons, was (still is) aggravated as combustion occurred in the larger toroidal volume of the bowl; near its periphery. Even improved pistons, rings and cylinder (or liner) materials, while improving the wear resistance, could not help move the rings to a higher position. Not that there was much interest to do so then; the deleterious effects of high headland clearances (from low-ring positions) had not been properly documented.
About 25 years ago, when the damaging effects of high headland clearance volumes were recognized, and acted upon by raising the ring pack, a new approach was taken to cool the area. This approach, called “top-liner cooling”, feeds water to the top of the liner, at its mounting flange; and works very-well to allow the raised “headland” rings. This approach has not been universally accepted; instead, interior cooling of the piston's ring-band area (cooling galleries) is used; with engine oil and various mechanisms to carry the oil to the high place on the piston undercrown. The approach increases the cost of the pistons; still, fails to allow “headland” rings. The ring-temperature dilemma is aggravated, on DI diesels, by the fact that the upper lip of the combustion bowl is only a short radial distance inboard from the cylinder diameter; and because the design of the piston crown does not allow the cooling galleries to reach high-enough to permit the “headland rings”; further increasing the heat transfer to them and raising their temperature. This situation cannot be helped by better piston-ring gallery-cooling systems; not when the problem is the antiquated combustion system generating far too-much heat in the upper peripheral areas of the pistons.
On current DI engines, it is the convention to include a squish-area; formed between the periphery of the piston crown and the fire-deck, to generate squish turbulence in the chamber and increase the in-bowl swirl to accelerate combustion process. This was a fine idea thirty years ago, when injection started early to accommodate the long duration of the injection period; then caused by ancient low-pressure injection systems. Those systems were characterized by combustion-initiation taking place much-before TDC; to avoid combustion termination being very-late, because this reduced the power output and increased the fuel consumption and smoke. Today, when high-pressure, short-duration injection systems initiate injection and combustion at, or near, TDC; the use of swirl is already obsolete, as squish-and-swirl turbulence, generated about one engine revolution earlier than combustion, are largely ineffective after TDC; and energy is saved by not generating them. Our new combustion system discards this old swirl approach, and uses new accelerating mechanisms to produce a late, but fast combustion process.
Today, there are two different approaches to designing the relative position of the valve head in relation to the cylinder head fire-deck, the combustion chamber, and the piston itself; these approaches result from the different preferences of the engine designers themselves. Some designers prefer to have the entire valve head, on each valve, protruding below the head's fire-deck. The advantage of this design is that air-flow starts into the cylinder immediately after the intake valve(s) starts to open; or the exhaust-gas flow begins evacuating the cylinder immediately after the exhaust valve(s) begins to open. The same effect takes place as the valves close; air or gas flow continues uninterrupted until the valves effectively close by seating. This design reduces the pumping losses and makes for a more-efficient thermodynamic cycle. One disadvantage is that, during the many overhauls and repairs that heavy-duty engines are required to endure, and while manhandling the cylinder heads; the valve-heads, protruding below the fire-deck, may get damaged. Another disadvantage is that, to provide “bump” clearance between the valve head and the piston, piston notches are necessary; and, apart from interfering with the air-swirl motion required by today's modern DI engines, machining the notches cost money.
Some engine designers, however, prefer to totally recess the valve heads into the fire-deck of the cylinder head; to avoid the need of forming notches on the piston top (because they interfere with the air swirl), as well as the possibility of damaging the valve heads during overhauls or repairs. Under these conditions, however, flow through the valves, in or out of the cylinders, is shrouded by the encirclement of the valve head(s) inside the recesses on the cylinder head's fire-deck.
One premise of this invention is that, if current large diesel engines used very-small tip-discharge orifices, they would have much better startability and idle operation, with less noise, fuel consumption and NOx; as explained in the aforementioned SAE Paper 2001-01-0278. Currently, tip-discharge orifices about 0.25–0.3 mm are used by industrial and truck-type DI engines. Smaller holes, about 0.14–0.18 mm have been successfully-used on very-small passenger-car DI engines; but only with low-Sulphur European fuels. These smaller orifices; smaller than the Pintaux single auxiliary-spray hole of 1939, have not shown the same coking tendencies of the Pintaux; because they work on the always-leaner, cleaner, cooler environment of the DI chamber. As the smaller nozzle-tip discharge holes improve the startability, if they were used on larger truck engines, the high CRN in-use today would not be required, and the engines would run with lower Pmax; reducing the BSFC and BSNOX. The problem, though, is that with all-small holes, the hypothetical new nozzle would lack discharge capacity to carry full-load fuel. This application shows how this new problem is solved by new variable-flow tips that restrict the early fuel-flow; to produce smooth, quiet starts; but which then open to full flow to allow the engine to carry full-load. This is what throttling-pintle nozzles have been doing for almost 75 years on Divided-Chamber engines. Such tips, however, because they discharge along their main axis (which with multi-valve engines is also the main cylinder axis), cannot be used on shallow-bowl DI engines, which need multiple discharge orifices with large included angles of 140° or more.